How to know if protection relay contacts can trip circuit breaker trip coil directly (no trip relay)

[electrical429]

Just want to make sure that I am looking at the right thing. Protection relay output contact spec says the following:

Make & Break Capacity:
DC: 50 W resistive
DC: 62.5 W inductive (L/R = 50 ms)
AC: 2500 VA resistive (cos φ = unity)
AC: 2500 VA inductive (cos φ = 0.7)

I assume that if circuit breaker trip coil has a burden of >62.5 W then we need to use either trip relay or protection relay with high make/break contacts such as the following:

Make & Break Capacity:
DC: 7500 W resistive
DC: 2500 W inductive (L/R = 50 ms)

 

[LionelHutz]

Yes, correct. You may want to do it anyways so you don't eventually damage the protection relay which would be harder and more expensive to repair compared to swapping a relay.

 

[stevenal]

Generally, the circuit breaker will route the trip circuit through an auxiliary switch contact that will interrupt the inductive load when the breaker opens.

 

[cranky108]

Yes generally, the circuit breaker will have an interrupting contact built in. In this case you only need to worry about make and carry current.
But SEL does make a contact extender, that will transfer the contact to a solid-state circuit, and then snuff out the breaking in an electronic circuit.

Other options is to use two contacts in series.

 

[electrical429]

Ok, but how do interruptive contacts fit in the picture? Say I have a relay with contacts rated for make & break capacity of 50W resistive and 65W inductive. Assume that trip coil is 100W. Even if circuit breaker interrupts the trip coil load when the CB opens wouldn't protection relay contacts still have to make 100W trip coil load first which will be higher than its rating?

 

[cranky108]

Make and carry rating is generally higher than the interrupting rating.
Example, most lockouts don't even have an interrupting rating. Only a make and carry rating.
But is your make and carry needs are greater than your relay contacts, use an aux relay.

 

[electrical429]

Ok, so based on the full contact spec below, are you saying that I should be looking at Make, Carry rating rather than Make & Break Capacity? i.e. if the trip coil is 110W then current will be 110W/110V=1A, therefore protection relay contacts are suitable to operate trip coil directly? And by the same logic if the trip coil burden would be 3300W then we could still operate trip coil directly as the current would be 3300W/110V=30A?

Continuous Carry Ratings (Not Switched):
Maximum continuous current: 10 A (UL: 8 A)
Short duration withstand carry: 30 A for 3 s or 250A for 30ms
Rated voltage: 300 V

Make & Break Capacity:
DC: 50 W resistive
DC: 62.5 W inductive (L/R = 50 ms)
AC: 2500 VA resistive (cos φ = unity)
AC: 2500 VA inductive (cos φ = 0.7)

Make, Carry:
30 A for 3 secs, dc resistive, 10,000 operations (subject to the above limits of
make/break capacity and rated voltage)

Make, Carry & Break:
30 A for 200 ms, ac resistive, 2,000 operations (subject to the above limits of
make/break capacity & rated voltage)
4A for 1.5 secs, dc resistive, 10,000 operations (subject to the above limits of
make/break capacity & rated voltage)
0.5 A for 1 sec, dc inductive, 10,000 operations (subject to the above limits of
make/break capacity & rated voltage)
10 A for 1.5 secs, ac resistive/inductive, 10,000 operations (subject to the above
limits of make/break capacity & rated voltage)

 

[LionelHutz]

Again, yes up to 30A of make current is allowed, it says so right in the ratings.

 

[cranky108]

Beware of trip currents less than 1 amp. They can cause other problems.